1. Field of the Invention
The present invention relates to an electronic ballast of a high power factor for a compact fluorescent lamp (CFL), and more particularly, to an electronic ballast of a high power factor for a compact fluorescent lamp (CFL) capable of implementing a high power factor and turning on lamps of different capacitances (3W-26W) or selectively turning on two lamps having the same capacitance or one lamp, using one circuit, by replacing a switching transistor with a field effect transistor and separating a lamp power and a circuit driving power.
2. Background of the Related Art
In general, lighting fixtures that emit light such as an incandescent light, a fluorescent lamp, and the like are attached to given locations (in particular, ceiling) in an office, homes, buildings, and the like, in order to make bright surrounding environment when it gets dark. Those lighting fixtures are replaced with new ones after their power are run out.
The fluorescent lamp of these lighting fixtures might be classified largely into a transformer mode and a ballast mode.
A compact fluorescent lamp (CFL) that has been widely used has a ballast element and a screw element on the top of the lamp. It can be thus easily used as a socket for a common incandescent light.
The lamp socket of a socket type for use in the incandescent light, the fluorescent lamp, etc. has been widely used for interior illumination in common homes, offices, etc. or inner illumination within refrigerators, microwave ovens, etc.
However, the above lamp is expensive since respective lamps have ballasts installed thereto. Further, this kind of the lamp has problems that resources are unnecessarily wasted and environment is contaminated since the lamp its power is run out must be discarded.
Further, if a lamp having no ballast is to be used, a transformer or an electronic ballast in addition to a socket must be provided. However, the volume of the transformer or the electronic ballast is large. Due to this, there is a problem that the productivity is low since they are difficult to install within the lamp.
In order to solve the mentioned problems encountered in the conventional compact fluorescent lamp, there was proposed a ballast socket for the compact lamp in which a printed circuit board integrated with various circuit components is mounted within the socket in order to improve the productivity.
FIG. 1 is a circuit diagram of the conventional electronic ballast for the compact fluorescent lamp according to one embodiment of a prior art.
As shown in FIG. 1, a photocell circuit unit 100 includes a power supply unit 101 for supplying a power, a varistor B1 connected between both ends of the power supply unit 101 for stabilizing an AC (alternating current) power inputted thereto, a fuse F1 that is short-circuited in order to prevent in advance damage of the circuit due to a high voltage when an AC power inputted thereto exceeds a predetermined voltage, a DC transformer 103 for rectifying the AC power outputted from the power supply unit 101 and then outputting it as a DC power, a photoelectric device PC connected to the DC transformer 103, for transforming the output voltage of the DC transformer 103 as a resistance value of the photoelectric device PC becomes low when the photoelectric device is exposed to bright environment and a resistance value of which becomes high when the photoelectric device is exposed to dark environment, first and second amplifiers 105 and 107 connected to the photoelectric device PC, for comparing the reference voltage and a voltage changed depending on an internal resistance value of the photoelectric device PC and then amplifying the difference voltage, a thyristor (SCR) 109 connected to the first and second amplifiers 105 and 107, for switching the voltage outputted from the first and second amplifiers 105 and 107, a bridge diode (BD) 111 connected to the thyristor 109, for rectifying the voltage outputted from the thyristor 109, and a triac TA1 connected to the bridge diode 111, for supplying the power to a DC transformation unit 200 or blocking the power applied to the DC transformation unit 200.
A DC transformation unit 200 includes a bridge diode (BD) and smoothing condensers C5 and C6 for rectifying the AC power supplied from the photocell circuit unit 100 to be a DC power.
Further, a CF lamp driving circuit unit 300 includes power transistors T1 and T2 connected to the bridge diode (BD) and the smoothing condensers C5 and C6 in the DC transformation unit 200, for turning on the CF lamp, oscillation coils L1, L2 and L3 connected to the power transistors T1 and T2, for generating a frequency of 25 Khz˜30 Khz depending on the values of the coils, a bulb BULB connected to the oscillation coils L1, L2 and L3, for turning on the CF lamp using a voltage of a high frequency, a condenser C10 connected between the oscillation coil L3 and the bulb BULB, for offsetting a surge voltage occurring when the lamp is connected to the socket in order to protect the lamp and the socket, and a thermistor switch 301 for sensing the temperature within the socket and then putting out the lamp when the sensed temperature is higher than the reference temperature.
In the above, the CF lamp driving circuit unit 300 further includes a plurality of diodes D5, D6, D7, D8 and D9 for protecting the power transistors T1 and T2, and a triac TA2 for preventing line surge from being applied to the base of the power transistor T2.
An operation of the conventional electronic ballast for the compact fluorescent lamp constructed above will be below described.
First, the photocell circuit unit 100 receives an AC power for common use (AC120V˜AC220V) and then determines whether the photoelectric device PC has to be turned on depending on the intensity of surrounding radiation. If it is determined that the photoelectric device PC has to be turned on, the bridge diode (BD) and the smoothing condensers C5 and C6 in the DC transformation unit 200 convert the AC power into a DC power. The power transistors T1 and T2 in the CF lamp driving circuit unit 300 are repeatedly turned on and off according to the DC power. Accordingly, the oscillation coils L1, L2 and L3 cause high-frequency oscillation, so that the lamp is turned on by the high frequency generated thus.
Meanwhile, if surrounding environment of the photocell circuit unit 100 is bright, the power applied to the DC transformation unit 200 or the CF lamp driving circuit unit 300 is blocked, so that the lamp is not turned on. If surrounding environment of the photocell circuit unit 100 is dark, the photoelectric device PC turns on the triac TA1 being a switching device.
At this time, if surrounding environment is dark than about 10LUX˜30LUX, the resistance value of the photoelectric device PC becomes high. Also, the photoelectric device PC inputs a voltage higher than the reference voltage to the first and second amplifiers P1 and P2 in the first and second amplifiers 105 and 107.
Next, the first and second amplifiers P1 and P2 compare the voltage with the reference voltage and then amplify the difference voltage by a given level to output the resulting voltage to the gate of the thyristor (SCR) 109. At this time, the condenser C2 of the second amplifier P2 plays an important role in preventing that the lamp is put out when surrounding environment becomes instantly bright while the lamp is turned on.
Further, the thyristor 109 performs a switching operation according to the voltage applied to the gate thereof and thus controls the operation of the bridge diode 111.
In addition, the DC transformer 103 in the photocell circuit unit 100 receives the power outputted from the power supply unit 101, makes smooth the voltage as a DC power, and then supplies the resulting power to the first and second amplifiers 105 and 107 and other circuits.
Meanwhile, the AC power applied to the DC transformation unit 200 is rectified as a DC power by means of the bridge diode BD and the smoothing condensers C5 and C6.
Further, the DC transformation unit 200 outputs the voltage that was rectified as the DC power, to the power transistors T1 and T2 through the resistor R11, the diode D5, the condenser C7 and the triac TA2 in the CF lamp driving circuit unit 300.
At this time, the power transistors T1 and T2 are alternately driven each other.
In particular, the power transistors T1 and T2 oscillate in a frequency of 25 Khz˜30 Khz depending on the values of the oscillation coils L1, L2 and L3 connected to the bases of the power transistors T1 and T2. These oscillation voltages result in supplying an instantly high voltage through the coil (CT) and the condenser C9 of the bulb BULB, to both ends of the lamp.
Therefore, the lamp is turned on while a gas is ionized within the lamp.
Further, the condenser C10 connected between the oscillation coil L3 and the bulb BULB offsets the surge voltage occurring when the lamp is connected to the socket, whereby flickering of the lamp is removed.
Also, the thermistor switch 301 senses the temperature within the socket and blocking the power being applied to the CF lamp driving circuit unit 300 when the sensed temperature is higher than the predetermined temperature, thus putting out the lamp.
FIG. 2 is a circuit diagram of a conventional electronic ballast for 120V according to the other embodiment of the prior art.
As shown in FIG. 2, the electronic ballast includes the power supply 601; a power supply unit 610 having a fuse F that is short-circuited in order to prevent in advance damage of the circuit due to a high power when the voltage of the power supply 601 exceeds a predetermined voltage, a varistor B1 connected between both supply ends of the power supply 601 for stabilizing an AC power, a filter 611 for removing noise from the power, and a plurality of condensers C1˜C3 for voltage stabilization; a DC transformation and boosting unit 700 having diodes D12 and D13 and condensers C13 and C14 for rectifying the AC power (120V) supplied from the power supply unit 610 to be a DC power and then boosting it twice; and a lamp driving unit 300 that oscillates according to the power supplied from the DC transformation and boosting unit 700 to turn on the lamp.
In the above, the lamp driving unit 300 includes power transistors Q1 and Q2 connected to the DC transformation and boosting unit 700, for performing a switching operation in order to produce an oscillation voltage for turning on the fluorescent lamp, oscillation coils L1, L2 and L3 connected to the power transistors Q1 and Q2, for generating a frequency of 25 Khz˜30 Khz depending on the values of the coils, a bulb BULB connected to the oscillation coils L1, L2 and L3, for turning on the fluorescent lamp using a voltage of a high frequency, diodes D10 and D11 and condensers C10 and C11, which are connected between the oscillation coil L3 and the bulb BULB, for offsetting a surge voltage occurring when the lamp is connected to the socket in order to protect the lamp and the socket, a plurality of diodes D5˜D9 for protecting the power transistors Q1 and Q2, and a triac TA1 for preventing line surge applied to the base of the power transistor Q2.
An exemplary operation of the fluorescent lamp for the electronic ballast constructed above will be below described.
AC 120V of the power supply 601 is inputted to the power supply unit 610. In the power supply unit 610, the filter 611 filters the AC power through the fuse F to remove line noise from the AC power. Next, the plurality of the condensers C1˜C3 stabilize the AC power and then transmit the stabilized AC power to the DC transformation and boosting unit 700.
In the DC transformation and boosting unit 700, the diodes D12 and D13 rectify the AC power to be a DC power. Next, the condensers C13 and C14 boost the DC power twice and then transfer it to the lamp driving unit 300.
In the lamp driving unit 300, the power transistors Q1 and Q2 are repeatedly turned on and turned off according to the DC power. Accordingly, high frequency oscillation occurs through the oscillation coils L1, L2 and L3, which turns on the lamp.
In other words, the DC power that was boosted to the DC power twice in the DC transformation and boosting unit 700 is transferred to the power transistors Q1 and Q2 via the resistor R11, the diode D5, the condenser C7 and the triac TA1. Also, the power transistors Q1 and Q2 are alternately operated according to the DC power.
In particular, the power transistors Q1 and Q2 oscillate in a frequency of 25 Khz˜30 Khz depending on the values of the oscillation coils L1, L2 and L3 connected to the bases of the power transistors Q1 and Q2. This oscillation voltage results in supplying an instantly high voltage through the coil CT and the condenser C9 of the bulb BULB, to both ends of the lamp. Therefore, the lamp is turned on while a gas within the lamp is ionized.
Further, the diodes D10 and D11 and the condensers C10 and C11, which are connected between the oscillation coil L3 and the bulb BULB, offset the surge voltage occurring when the lamp is connected to the socket, whereby flickering of the lamp is removed.
In the first and second embodiments, however, the power supply of the circuit that oscillates at high frequency to drive the lamp and the lamp power supply for turning on the lamp is utilized as single power supply. Due to this, the first and second embodiments have disadvantages that the power factor is low and the overall operation of the circuit is unstable due to interference, etc.
Also, the second embodiment has disadvantages that only one lamp could be turned on and additional circuit for emitting heat is not designed.